1. Field of the Invention
The present invention relates to a preparation method of a toner having a micro radius, and more particularly, to a preparation method of a toner based on a process including an emulsion polymerization, to prepare a toner having a micro radius, so that an effective resolution image may be achieved by an electrophotographic image forming apparatus.
2. Description of the Related Art
Electrophotographic image forming apparatuses include fax machines, LED or LCS printers, digital printers, laser printers, or laser copiers. These apparatuses use toner compositions containing a colorant, a binder resin, a charge control agent, and other functional additives.
Colorants are largely divided into dye colorants and pigment colorants. The pigment colorants, compared to the dye colorants, have an excellent thermal stability and light fastness and thus, are used more often as toner colorants.
The binder resin corresponds to about 90% of the entire toner composition, and its main function is to bind toner particles onto a recording medium. There are many types of polymers that are eligible for use as the binder resin, but a colloid gel type latex with its two components being dispersed to particles is usually used as the binder resin.
The charge controller agent is employed to control the quantity of electric charge on toner particles. Examples of the charge controller agent include metal azo compounds, salicylic acid metal complexes, nigrosine, and quaternary ammonium salts.
Among the functional additives contained in the toner is a releasing agent which gives a neat and quick release. Particularly, the releasing agent is used to more easily release a roller from a toner when a toner image is transferred onto a recording medium, and thus, to prevent a toner offset. Many times, the recording medium adheres to the roller due to the toner, causing the recording medium to be caught in the middle. Hence, the releasing agent is added to the toner composition.
Typically used releasing agents are a polyolefin group having low molecular weight, a silicon group having a softening point by the application of heat, a fatty acid amid group, and wax.
In an electrophotographic image forming apparatus, a toner particle size is a key factor that determines the resolution of a final print image. The more uniform and spherical the toner particles are, and if the toner particles have a micro size, the higher the resolution of a final print image can be.
The preparation methods of a dry toner for use in the electrophotographic image forming apparatus are largely divided into two types: milling and polymerization. The polymerization is further divided into a suspension polymerization and an emulsion polymerization. The milling process, by its nature, is not suitable for making the toner particles spherical in a uniform size. The suspension polymerization has also its limits with respect to obtaining micro size toner particles.
According to the toner preparation method based on a general emulsion polymerization, an emulsion is first prepared with a binder resin, a colorant, and a releasing agent, each component having less than a 1 μm particle size, and later a coagulant is added to the emulsion for aggregation. In this manner, the emulsion is primarily aggregated in a size of 1-3 μm. Next, the emulsion is secondarily aggregated with a latex having a different molecular weight to prepare toner particles in a size between 5 μm and 15 μm.
The emulsion polymerization is well disclosed in U.S. Pat. Nos. 6,120,967, and 5,863,696. In the disclosures, a coagulant is used to aggregate a resin latex, a pigment, and a wax emulsion particle. At first, a latex having a size of 100 nm to 200 nm was aggregated until its size ranged between 1 μm and 3 μm. Then, the latex was subjected to a secondary aggregation process or a melting process. However, this method was not adequate to obtain spherical particles. Moreover, the aggregation and melting processes are very complicated, and have several technical difficulties in adjusting particle size and obtaining spherical particles. Especially, the melting process requires a 2 to 4 hour-heating period. As a result, the entire process becomes very lengthy and complicated.
Therefore, there is a need to develop a new, simple preparation method of spherical microsize toner particles.